The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Audio Video Bridging (AVB), is a set of standards developed and being developed by the Institute for Electrical and Electronics Engineers (IEEE) 802.1 working group with the intent of supporting real-time traffic, such as audio traffic and video traffic, with defined latencies and guaranteed delivery.
This is a change in direction as compared to past communication network protocols, such as the IEEE 802.3 Ethernet standard and the IEEE 802.11 wireless local area network (WLAN) standards, that are designed to be ‘best effort’ protocols. ‘Best effort’ here means that there are no guarantees of delivery nor is the latency through the network reasonably definable. These older Ethernet and WLAN networks are allowed to drop (or discard) data at Layer 1 and/or Layer 2, and it is the responsibility of higher layer protocols in the protocol stack to insure reliable delivery of data by the re-transmission of the dropped portions. Such re-transmissions insure users get the full content of their e-mails and other file transfers, but the re-transmissions do not help when the data is time sensitive such as audio and/or video streams. Re-transmission cannot be done in these cases as the window of usage of the information has usually past (i.e., the re-transmitted data typically shows up too late to help).
A phone conversation is an example application that uses real-time audio. The quality of a phone connection is typically excellent when making a POTS (Plain Old Telephone System) call. However, the same call using via the Internet is generally not as good and may not be acceptable at the present day. This is because a POTS network guarantees enough bandwidth for each call with defined latencies. The Internet currently cannot provide such guarantees.
A goal of AVB is to support real-time data streams with defined latencies and guaranteed delivery, over Ethernet- and WLAN-type networks, while at the same time allowing the previous (and future) applications to continue functioning on these same networks.
Devices configured to operate according to AVB (AVB devices) periodically exchange timing information that allows both ends of a link to synchronize their time base reference clock very precisely. This precise synchronization allows synchronization of multiple streams and provides a common time base for sampling/receiving data streams at a source device and presenting those streams at the destination device with the same relative timing.
AVB utilizes stream reservations to help insure that an AVB stream can start (or be joined to) only if all the bridges in the path of the stream have sufficient resources to support the stream. Resources include available buffers and bandwidth of the links. Additionally, AVB reservations help insure that no more than 75% of a link's bandwidth (as a default) is used for AVB streams. This helps insure the applications of the network can continue to function as before.
AVB also utilizes stream shaping to define how AVB data should be transmitted in the absence of congestion. Traffic shaping is a process of smoothing out the traffic for a stream so that the packets making up the stream are evenly distributed in time. If traffic shaping is not done at sources and bridges, then packets of a stream tend to “bunch” into bursts of traffic that can overwhelm buffers in subsequent bridges, switches and other infrastructure devices. AVB implements traffic shaping using existing IEEE 802.1Q forwarding and priority mechanisms but also defines a particular relationship between priority tags and frame forwarding behavior at endpoints and bridges.